This disclosure relates to devices and methods for hydrogen storage and recovery.
Hydrogen is a “clean fuel” because it can be reacted with oxygen in hydrogen-consuming devices, such as a fuel cell or a combustion engine, to produce energy and water. Virtually no other reaction byproducts are produced in the exhaust. As a result, the use of hydrogen as a fuel effectively solves many environmental problems associated with the use of fossil-fuels. Safe and efficient storage of hydrogen gas is, therefore, an important feature for many applications that can use hydrogen. In particular, minimizing volume and weight of the hydrogen storage systems are important factors in mobile applications.
Several methods of storing hydrogen are currently used but these are either inadequate or impractical for wide-spread consumer applications. For example, hydrogen can be stored in liquid form at very low temperatures. Cryogenic storage, however, provides a low volume density of hydrogen storage per liter, and is insufficient for consumer applications. In addition, the energy consumed in liquefying hydrogen gas is about 30% of the energy available from the resulting hydrogen. Finally, liquid hydrogen is neither safe nor practical for most consumer applications.
An alternative is to store hydrogen under high pressure in cylinders. However, a 45 kilogram steel cylinder can only store about one pound of hydrogen at about 154 kilogram/square centimeter (kg/cm2), which translates into 1% by weight of hydrogen storage. More expensive composite cylinders with special compressors can store hydrogen at higher pressures of about 316 kg/cm2 to achieve a more favorable storage ratio of about 4% by weight. Although even higher pressures are possible, safety factors and the high amount of energy consumed in achieving such high pressures have compelled a search for alternative hydrogen storage technologies that are both safe and efficient.
Hydrogen can also be stored in several types of solid-state materials. The reversible storage of hydrogen in solid-state materials depends on the thermodynamic and kinetic properties of the storage material to absorb, dissociate, and react reversibly with hydrogen to form the hydrogen storage material. There are several modes and mechanisms in which hydrogen storage can occur if the chemical potentials and kinetics are favorable toward hydriding, complexation or hydrogen sorption. In some cases alloying or forming composite materials can favorably alter the thermodynamics of potential hydrogen storage materials. Also the “doping” of catalyst into hydrogen storage materials has been shown to improve reaction rate and decrease activation energy for the reversible hydrogen storage reaction. Although these materials strategies can improve the overall performance of several types of storage materials, there has not been an effort to generally exploit these chemical and thermodynamic properties across a wide range of storage materials.
In view of the above, there is a need for safer, more effective and efficient methods of storing and recovering hydrogen. In the case of solid-state hydrogen storage materials there is a need to improve the thermodynamic and kinetic properties of storage materials to decrease sorption and desorption energy requirements, while maintaining a sufficient hydrogen charge and discharge rate. In addition, there is a desire to minimize the overall system volume and weight.